What it is
Mean arterial pressure (MAP) is the average blood pressure in the arteries over a single cardiac cycle. It is the pressure that actually drives perfusion to organs, which is why it — rather than systolic pressure alone — underpins targets for cerebral perfusion pressure and shock resuscitation. Because the heart spends roughly two-thirds of the cycle in diastole at normal rates, MAP sits closer to the diastolic than the systolic value.
The formula
MAP = DBP + ⅓ × (SBP − DBP)
The term (SBP − DBP) is the pulse pressure; one-third of it is added to diastole. This is the standard cuff-based estimate and is accurate at normal heart rates.
When to use it
- Setting and tracking a perfusion target in shock, sepsis, or after cardiac surgery.
- Calculating cerebral perfusion pressure (CPP = MAP − ICP) in raised-ICP or TBI management.
- Comparing a measured MAP against age-specific norms to gauge adequacy of perfusion.
Worked example
A child has a blood pressure of 90/60 mmHg.
- Pulse pressure = 90 − 60 = 30 mmHg
- MAP = 60 + (30 / 3) = 60 + 10 = 70 mmHg
Note how MAP (70) is much nearer the diastolic (60) than the midpoint (75) — the diastolic weighting in action.
Pitfalls
- The ⅓ weighting assumes a normal heart rate. At marked tachycardia, diastole shortens and true MAP rises toward the midpoint; the formula underestimates. An invasive arterial line gives the true integrated MAP.
- Use age-appropriate targets. A “normal-looking” adult MAP of 65 may be inadequate for an adolescent and is meaningless without the child’s baseline. A rough lower acceptable bound is the 5th-percentile MAP for age (and approximately gestational age in mmHg for neonates).
- Cuff MAP is an estimate. Wrong cuff size, motion, and arrhythmia degrade accuracy — corroborate with clinical perfusion (cap refill, urine output, mentation).
- MAP alone doesn’t tell you flow. Adequate pressure with poor cardiac output can still under-perfuse.
Run it: Mean Arterial Pressure (MAP): The DBP + ⅓(SBP − DBP) Estimate
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.